As a method for producing a Silicon on Insulator (SOT) wafer, in particular, a method for producing a thin-film SOI wafer that can enhance the performance of a leading-edge integrated circuit, a method for producing a SOI wafer by delaminating an ion implanted wafer after bonding (an ion implantation delamination method: the technology also called SmartCut® process) has attracted attention.
This ion implantation delamination method is the technology of producing a bonded SOI wafer by forming an oxide film on at least one of two silicon wafers and implanting gas ions such as hydrogen ions or rare gas ions from the upper surface of one silicon wafer (a bond wafer) and thereby forming an ion implanted layer (also called a microbubble layer or an encapsulated layer) in the wafer, then bringing the implanted surface into intimate contact with the other silicon wafer (a base wafer) with the oxide film placed therebetween, and then delaminating the one wafer (the bond wafer) in the form of a thin film by using the microbubble layer as a cleavage plane by performing heat treatment (delamination heat treatment). Moreover, there is a method of achieving firm bonding by performing heat treatment (bonding heat treatment) on the SOI wafer subjected to delamination (refer to Patent Document 1).
At this stage, the cleavage plane (the delaminating plane) is the surface of a SOI layer, and a SOI wafer whose SOI film thickness is small and has a high degree of uniformity is obtained with relative ease. However, a damaged layer caused by ion implantation is present on the surface of the SOI wafer subjected to delamination, and the surface roughness is greater than that of a mirror surface of a normal silicon wafer. Thus, in the ion implantation delamination method, it is necessary to remove such a damaged layer and surface roughness.
As one of the methods for removing such a surface roughness or a damaged layer of the SOI layer surface, there is an annealing technique of performing high-temperature heat treatment in an argon-containing atmosphere. This annealing technique makes it possible to maintain high film thickness uniformity of the SOI layer obtained by the ion implantation delamination method while flattening the SOI layer surface (Patent Documents 1 and 2).